Process for bonding the fibers of a non-woven textile fabric

ABSTRACT

A BONDED NON-WOVEN TEXTILE FABRIC IS MADE BY INCORPORATING IN THE FABRIC AN AQUEOUS THERMOSENSITIVE LIQUID CONTAINING AN ELASTIC POLYMER CAPABLE OF BINDING THE FIBERS OF THE FABRIC AND THE POLYMER IS DIFFERENTIALLY COAGULATED THROUGHOUT THE THICKNESS OF THE FABRIC BY APPLYING COAGULATING HEAT CONDITIONS TO ONE SURFACE AND NONCOAGULATING HEAT CONDITIONS TO THE OTHER SURFACE, THE COAGULATING HEAT CONDITIONS BEING INDUCED BY A HEAT-CARRYING LIQUID, AND UNCOAGULATED POLYMER BEING THEN REMOVED BY WASHING OUT.

United States Patent 3,776,799 PROCESS FOR BONDING THE FIBERS OF A NON-WOVEN TEXTILE FABRIC Ehrenfried Gruber, Wiesbaden-Biebrich, Ludwig Klenk,

Hallgarten, and Klaus-Dieter Hammer, Finthen, Germany, assignols to Kalle. Aktiengesellschaft, Wiesbaden- Biebrich, Germany No Drawing. Filed May 2, 1972, Ser. No. 249,543 Claims priority, application Germany, May 5, 1971,

P 21 22 142.1 Int. Cl. C09j /00 US. Cl. 156-305 3 Claims ABSTRACT OF THE DISCLOSURE This invention concerns improvements in bonded nonwoven textile fabrics.

For bonding the fibres of non-woven textile fabrics there exist a number of processes, which may be enuerated as follows:

(i) Fibre bonding by welding fibres at their crossing points. I

(ii) Solvent bonding.

(iii) Bonding by incorporating a synthetic polymer into a fibre fleece.

(iv) Bonding by needle-punching the non-woven fabric.

(v) Any combination of the above processes.

In processes in which a fleece is bonded by incorporating chemical binders, in particular the method of polymer coagulation from a polymer solution or dispersion preseats a major problem.

. It is known to eflect coagulation by the action of hot air upon the non-woven material moist with hinder or by passing the impregnated material over heated drums. It is also known to coagulate the polymer binders by passing the non-woven product, impregnated with binding liquid, over perforated drums and by simultaneously drawing hot air through the surface of the drum. Coagulation by infrared irradiation or by the action of an electric high-frequency field. on the non-woven fabric impregnated with binding liquid is also known, as also are combinations of the above coagulation techniques.

The known processes have in practice, however, the disadvantage that only relatively low coagulation rates can be achieved or that'in the case of high-frequency action, although the coagulation rate is high, the disadvantages caused by rapidevaporation of the liquid portion of the binding agent are nevertheless considerable. Vapour bubbles forcing their way from the interior to the surface of the non-woven fabric entrain the coagulating polymer whereby hard films of binder may be formed on the surface.

Uncontrolled coagulation of binders in which the binding mass tends to accumulate on the surface of the nonwoven fabric, mostly in the form of an incrustation of binder which is therefore lost from the interior of the non-woven material, has a negative effect on the properties of the bonded non-woven fabric. Such non-woven materials are bonded unevenly, they have a hard feel, be-

3,776,799 Patented Dec. 4, 1973 have like cardboard when bent and rolled up and, in particular, they do not possess the draping quality required. Apart from this the surfaces of such non-woven fabrics are often spotted and unsightly.

For certain purposes of application of the bonded nonwoven fabrics a homogenous distribution of binder throughout the cross section of the non-woven fabric is not required. A fieecy reverse side of the non-woven fabric is to be desired for application of the bonded non-woven fabrics as outer materials without lining for clothing purposes. For further processing of the bonded non-woven fabric to a substitute for natural leather for clothing it is likewise desirable that the reverse surface should be similar to velvet.

The object of the present invention is to produce nonwoven fabrics without the disadvantages of the non-woven fabrics bonded according to the known processes and in which the concentration of a binding agent in the nonwoven fabric shows a continuous gradient in the direction from one to the other fabric surface. On account of this distribution of binding agent over the cross section, the non-woven fabric possesses particularly good properties for rolling and bending and good draping characteristics. A measure of this draping capability is the flexing resistance of the nonwoven fabric according to German Standard DIN 53362.

The invention accordingly provides a process for bonding the fibres of a non-Woven textile fabric, wherein there is incorporated in the fabric an aqueous thermosensitive liquid containing an elastic polymer capable of binding the fibres of the fabric and there is contacted with one surface of the fabric a heat-carrying liquid at a temperature sufficiently high to efiect coagulation of the elastic polymer while at the same time the other surface of the fabric is maintained at a temperature below the coagulation temperature of the liquid containing the elastic polymer.

The bonded non-woven fabric produced according to the process of the invention by chemical binding agent is characterized by the fact that the binding agent concentration in the region of the surface of the non-woven fabric on which the heat-carrying fluid acts is higher than that in the region of the other surface of the non-woven fabric.

For use in the process of this invention the known nonwoven fibre structures are suitable which consist of natural or of synthetic fibres or of mixtures of these fibres.

These non-woven fabrics may be carded non-woven fabrics, fabrics produced according to the aerodynamic principle, staple non-Wovens or non-Wovens produced according to the wet process. Particularly suitable are fleeces based on polyester and/ or polyamide fibres or filaments.

Suitable chemical binding agents for the process of the invention are elastic, synthetic or natural polymers which can be coagulated from aqueous dispersion under heat influence. Particularly suitable are polyacrylic and polymethacrylic acid esters, natural or synthetic rubbers and polyurethanes.

The binding liquid used in the process of the invention contains a proportion of polymer solids of 10 to 60 percent 'by weight of the total weight of the binding liquid.

The liquid of the binding agents consists of an aqueous dispersion of the said polymers which effect fibre binding.

In order to render the liquid containing binding agent thermosensitive, said liquid additionally contains chemical agent which sensitize the heat coagulation capacity of the polymers so that by the action of the heat-carrying liquid on the binding agent liquid incorporated in the non-woven fabric, the polymers contained in this latter liquid are coagulated.

The coagulation temperature of the thermo-sensitive binding agent liquid is in the range of 20-90" C., preferably in the range 30 to 50 C.

The coagulation temperature of the binding liquid depends on the polymer, on the concentration of the poly mer and on the type of the chemical agent and the concentration applied to the thermosensitive liquid.

In each individual case the optimum coagulation temperature may be ascertained by simple test.

For thermo-sensitizing, the well-known chemical agents for this purpose are suitable, e.g. those based on polysiloxanes (e.g. Coagulant WS of Farbenfabriken Bayer).

Preferred thermo-sensitized binding agent liquids are aqueous dispersions of polyacrylates or polymethacrylates and/or of mixtures of the said polymers and also aqueous dispersions of synthetic rubber based on butadiene-acrylonitrile co-polymers.

Preferred non-woven fabrics can be mechanically consolidated by needle-punching; they may have a stitching density, for example, of approximately 400 stitches per cm.

A continuous web of material may be used.

The process of the invention may thus be carried out by impregnating a web of non-woven fabric with the binding liquid, for example in a Foulard filled with this liquid.

The binding agent liquid may have a temperature of approximately 18 to 25 C.

After removing the impregnated non-woven fabric from the liquid it is freed from surplus liquid, e.g. by squeezing in the nip of a pair of rollers.

As stated, a heat-carrying liquid acts on one surface of the non-woven fabric impregnated with binding liquid, the temperature of the former liquid being sufiicient to effect coagulation of the polymer binding agent.

Suitable liquids are those which neither dissolve nor swell either the fibers of the non-woven fabric or the chemical binding agent. Liquids which can be mixed with water are preferred; particularly suitable are higher alcohols and polyalcohols, e.g. polyglycols. Water itself cannot be used as heat-carrying liquid as there would then be a danger that the polymers incorporated in the non-woven fabric would be washed out by treatment with Water at elevated temperature.

The heat-carrying liquid may have a temperature between 35 and 140 C., a temperature between 70 and 100 C. being preferred.

By the action of the heat-carrying liquid on the one surface of the non-woven fabric, this surface is brought to a temperature in the range of 35 to 100 C., preferably to 60-90 C.

While the heat-carrying liquid is acting on the one surface of the non-woven fabric impregnated with the binding agent liquid the other surface is maintained at a temperature below the coagulation temperature of the binding liquid.

The surface of the non-woven fabric subjected to cooling will usually be brought down to a temperature between 5 and 40 C.

Cooling of this surface of the non-woven fabric may.

be effected by bringing it into contact with a cooled surface, e.g. with the cooled surface of a roller. It is essential for the process of the invention that the surface of the fleece opposite to that on which the heat-carrying liquid is acting has a temperature below the coagulation temperature of the binding agent liquid.

The temperature of the heat-carrying liquid and the temperature of the cooling roller may vary depending on the speed of travel of the web, on the type on the nonwoven fabric and on the binding agent liquid used. After coagulation of the polymer in the non-woven fabric this is washed, for example with water, and afterwards dried. The drying may be effected in a drier or in a drying tunnel under the action of hot air at 100-180" C.

The following examples illustrate the invention but are not intended to limit it thereto:

EXAMPLE 1 The starting material is a needle-punched non-woven fibre web with 400 stitches/cm half of it consisting of polyethylene terephthalate fibres with a length of 32 mm. and a titre of 1.3 dtex. and half of polyamide fibres of a length of 40 mm. and a titre of 1.7 dtex.

The non-woven fabric has a weight per unit area of 250 g./cm. and a density of 0.150 g./cm.

The binding agent liquid comprises a 40% aqueous dispersion of a butadiene-acrylonitrile co-polymer. The binding agent liquid is adjusted to a coagulation temperature of approximately 36 C. by the addition of a thermosensitizing agent based on polysiloxane (e.g. Coagulant WS). The non-woven fabric is impregnated in a Foulard with the binding liquid. In order to remove excess of binding liquid the non-woven fabric is after impregnation squeezed out in the nip between a steel and a rubber roller at a linear pressure Pl=0.5 kg. /cm.. The non-woven fabric then contains binding agent liquid in a proportion of 30-70% referred to the total weight of the non-woven fabric.

The web is then led continuously via a deflecting roller (at a speed of 1.5 m./min.) around the surface of a cooled roller, the axial plane of which is horizontal. The temperature of the cooled roller is 32 C. One quarter of the circumference of the roller is immersed over its whole length in a tank filled with polyglycol 400 at a temperature of approximately C. After leaving the coagulation device the web is led into another tank, in which it is washed with water. The washed web is then fed into a tunnel drier and dried at C.

The proportion of binder in the non-woven fabric, referred to the total weight, is 50% The non-woven fabric is then submitted to splitting into two splits of about equal thickness. The split that has been exposed to the cooled surface has a binder content of 38 percent by weight while the other split has a content of 62 percent by Weight.

The percentage figures of the splits in this and the following examples refer to a layer of the non-woven fabric of equal thickness to the split but containing no binder.

EXAMPLE 2 A mixed fibre fleece with 50 parts of polyethylene terephthalate fibers and 50 parts of polyamide fibres, having a weight per unit area of 470 g./m. and a density of 0.200 g. per cm. is treated under the same process conditions as in Example 1. After splitting of the bonded non-woven fabric into two splits as in Example 1, the split including the surface subjected to the heat-carrying liquid has a binder content of 65 percent by weight, while the other split has a binder content of 35 percent by weight.

EXAMPLE 3 Example 2 is modified by using a non-woven fabric with a weight per unit area of 250 g./m. and the temperature of the cooling roller is reduced to +15 C. The binder migration is thereby intensified. After splitting the fabric according to Example 1, the binder content in each split is ascertained. The split with the surface that has been exposed to the action of the heat-carrying liquid has a binder content of 80 percent by weight, while the other split has a binder content of 20 percent by weight.

EXAMPLE 4 In a modification of Example 2, a non-woven fabric with a weight per unit area of 470 g./m. is likewise used The temperature of the cooling roller is reduced to 15 C. as in Example 3 in order to achieve an intensification of the binder migration.

After splitting the fabric according to Example I, the split with the surface on which the heat-carrying liquid had acted contains a binding agent proportion of 76 percent by weight and the other split a proportion of 24 percent by weight.

EXAMPLE 5 Example 2 is modified in that a binding agent bath with a solids content of 30 percent by weight is used with a non-woven fabric having a weight per unit area of 470 g./m. and of the same type.

Process conditions are as indicated in Example 1.

The bonded non-woven fabric has a binding agent content of 40 percent by weight as referred to the total weight of the non-woven fabric. After splitting the fabric according to the directions given in Example 1, the split with the surface which has been exposed to the heat-carrying liquid-contains a binding agent proportion of 75 percent by weight while the other split contains 25 percent by weight of binding agent.

It is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of the invention.

We claim:

1. A process for bonding the fibres of a non-woven textile fabric, comprising incorporating in the fabric an aqueous thermosensitive liquid containing an elastic polymer capable of binding the fibres of the fabric, contacting with one surface of the fabric a heat-carrying liquid at a temperature sufficiently high to effect coagulation of the elastic polymer while at the same time the other surface of the fabric is maintained at a temperature below the coagulation temperature of the liquid containing the clastic polymer, washing out uncoagulated polymer and drying the bonded fabric.

2. A process as claimed in claim 1, the said other surface being cooled below the coagulation temperature by bringing it into contact with the surface of a cooled roller.

3. A process as claimed in claim 1, wherein the temperature of coagulation of the liquid containing the polymer agent is to C. and the heat-carrying liquid has a temperature in the range of to C.

References Cited UNITED STATES PATENTS 3,034,927 5/ 1962 Fairclough' et al 117-140 WILLIAM A. POWELL, Primary Examiner US. Cl. X.R. 

